Each year about 17 million new automobiles are introduced into the U.S. market. More than 95% of these automobiles run on conventional internal combustion engines. Federal regulations requiring reduction in automobile emissions have led many major auto manufacturers to invest in the development of light-weight metals and alloys. It is estimated that weight reduction from using lighter materials could result in saving almost 100 billion gallons of gasoline and also result in a reduction of 6.5 billion gallons of carbon dioxide emissions per year, just for passenger cars in the U.S.
There are many other uses for high strength, light-weight metals and alloys. For example, in the biomedical sector, there is an emerging market for load-bearing, light-weight, and biocompatible materials to provide support after temporary implants are re-absorbed.
Magnesium alloys have shown promising performances. See, for example, U.S. Pat. No. 8,361,251; U.S. Patent Publication No. 2007/0204936 A1; Gelman Publication No. 102005033750 A1; U.S. Patent Publication No. 2014/0261911 A1; U.S. Patent Publication No. 2014/0249531 A1; U.S. Patent Publication No. 2014/0154341 A1; and International Patent Publication No. WO 2012/003502 A2.
Magnesium, being the lightest of all structural metals, is almost one quarter the density of steel and two-thirds the density of aluminum. These properties make magnesium an excellent green alternative to replace metals and polymers in a variety of applications. The major hurdle in the utilization of magnesium, however, is the lack of affordable alloy compositions that exhibit proper creep resistance, including at elevated temperatures.
Current benchmark magnesium alloys are mainly of the Mg—Al alloy family including, for example, AZ91D, AM50A, and AM60B; however, precipitates formed in these alloys are not thermally stable above 125° C., significantly limiting their service temperatures. Currently, the main alternative alloy for elevated temperature applications is AE42, a Mg—Al based alloy comprising rare earth elements that can be used at service temperatures up to 170° C. Above this temperature, there is an abrupt degradation of creep resistance.
Because most rare earth elements are imported from overseas, the cost associated with AE42 and other similar alloys is very high. Furthermore, in the defense and aerospace markets, foreign suppliers of rare earth elements necessary for fabrication of current high-temperature Mg alloys, make this core technology vulnerable to interruption.
Therefore, there remains a need for magnesium alloys that can be made from more readily-available elements that can also be used for high-temperature and other applications.